In the Instant Pot, add olive oil, ground Italian sausage, chopped onion, minced garlic, Italian seasoning, and beef bouillon. Sauté for about 5 minutes until the meat is mostly browned.

Turn off the sauté function. Layer the uncooked pasta noodles on top of the meat mixture. Pour the water, marinara sauce, and diced tomatoes over the noodles. DO NOT STIR.

Secure the lid and set the vent to sealing. Cook on high pressure for 7 minutes. Let the pressure release naturally for 5-10 minutes, then carefully quick release any remaining pressure.

Carefully open the lid. Stir the soup well to combine all ingredients. If using fresh spinach, stir it in now and let it wilt for 2 minutes.

Prepare the ricotta topping: In a small bowl, combine 1 cup ricotta cheese, 1/4 cup grated Parmesan cheese, 1 egg yolk, and a pinch of salt and pepper. Mix well.

Ladle the hot lasagna soup into bowls. Top each serving generously with a couple spoonfuls of the prepared ricotta mixture and a sprinkle of Parmesan cheese.